A standard bed construction which has been popular for some time includes a frame for supporting a box spring. The box spring, in turn, is designed to support a mattress. Mattresses are available in a variety of sizes and are also constructed in various ways. One such construction which has proved to be highly desirable includes the use of an innerspring comprising a plurality of discrete coil springs which can be encapsulated in individual fabric pockets joined together in a string. An assembly of this type is known as Marshall construction and is disclosed, for example, in U.S. Pat. No. 4,234,983, issued to Stumpf, the disclosure of which is incorporated herein by reference. Once the strings of coils are formed, they may be arranged in any desired fashion such as a chevron or other pattern to provide an innerspring assembly in which the individual springs all have longitudinal axes oriented parallel one to another and the springs are closely packed together in an array having a generally rectangular shape in plan with the ends of the springs lying in a common plane. A suitable quilted foam pad of preselected thickness may then be used to cover the innerspring and provide a generally planar surface on which a person can sleep. Preferably, the innerspring is covered on both sides and has fabric edging connecting the opposed surface covers, thereby defining a unitary mattress assembly.
Each coil is typically manufactured from a single steel wire that is coiled using an apparatus disclosed, for example, in U.S. Pat. No. 4,401,501 also issued to Stumpf, the disclosure of which is likewise incorporated herein by reference. The spring characteristic is defined, among others, by the wire size and spring dimensions (pitch, coil length, coil diameter, etc.) which can be selected according to the desired properties of the seating or resting surface of the article of furniture or mattress in a manner known in the art.
Although coils of the aforedescribed type have been used almost exclusively in the construction of seating or resting surfaces, they are not inexpensive and severely impair the seating or sleeping comfort if one or more springs malfunction, for example, break.
It would therefore be desirable to provide a spring construction that is less expensive to manufacture than a solid wire spring while retaining the advantageous performance characteristic of the solid wire speing.